1. Field of the Invention
The present disclosure relates generally to miniature dynamo type electrical generators and corresponding power sources, and more particularly, to miniature electrical generators and power sources for projectiles fired by guns, mortars and the like or hand grenades and the like.
2. Prior Art
Chemical reserve batteries have long been used in various munitions, weapon systems and other similar applications in which electrical energy is required over relatively short periods of times. In addition, unique to the military is the need for munitions batteries that may be stored for up to twenty years without maintenance. Reserve batteries are batteries designed to be stored for years, even decades, without performance degradation. Reserve batteries are stored in an inert state and can be activated within a fraction of a second with no degradation of battery capacity or power. Typical Reserve batteries are thermal batteries and liquid reserve batteries.
The typical liquid reserve battery is kept inert during storage by keeping the electrolyte separate from the electrodes. The electrolyte is kept in a glass or metal ampoule inside the battery case. Prior to use, the battery is activated by breaking the ampoule and allowing the electrolyte to flood the electrodes. The ampoule is broken either mechanically or by the high g shock experienced from being shot from the cannon.
Thermal batteries represent a class of reserve batteries that operate at high temperatures. Unlike liquid reserve batteries, in thermal batteries the electrolyte is already in the cells and therefore does not require a distribution mechanism such as spinning. The electrolyte is dry, solid and non-conductive, thereby leaving the battery in a non-operational and inert condition. These batteries incorporate pyrotechnic heat sources to melt the electrolyte just prior to use in order to make them electrically conductive and thereby making the battery active. Thermal batteries have long been used in munitions and other similar applications to provide a relatively large amount of power during a relatively short period of time, mainly during the munitions flight. Thermal batteries have high power density and can provide a large amount of power as long as the electrolyte of the thermal battery stays liquid, thereby conductive.
Reserve batteries are expensive to produce, primarily since the process of their manufacture is highly labor intensive and involve mostly manual assembly. For example, the process of manufacturing thermal batteries is highly labor intensive and requires relatively expensive facilities. Fabrication usually involves costly batch processes, including pressing electrodes and electrolytes into rigid wafers, and assembling batteries by hand. The reserve batteries are encased in a hermetically-sealed metal container that is usually cylindrical in shape. In munitions, thermal batteries may be initiated during launch via inertial or electrical igniters, or may be initiated later during the flight via electrical igniters. The liquid reserve batteries are usually activated during launch by breaking the electrolyte ampoule.
Chemical reserve batteries, including thermal batteries and liquid reserve batteries, are generally very expensive to produce, require specialized manufacturing processes and equipment and quality control, and are generally required to be developed for each application at hand.
All existing and future smart and guided weapons, including gun-fired projectiles, mortars, and small and large gravity dropped weapons, require electric energy for their operation. For many fuzing operations such as fuzing “safe” and “arm” (S&A) and sensory functionalities and many other “smart” fuzing and initiation functionalities, the amount of electrical energy that is needed is low and may be as low as 10-50 mJ, and even less. In fact, with such electrical energy levels, low-power electronics could be easily powered to provide the above fuzing or the like functionalities. The amount of power required to operate many other electronic components, for example those used for diagnostics and health monitoring purposes, or for receiving a communicated signal or the like is also very small and can be readily achieved with electrical energy in the above range. In all such applications, particularly for powering electronics for fuzing and other similar “safe” and “arm” functionalities, it is highly desirable to have low-cost and safe alternatives to chemical reserve batteries. This is particularly the case for the above applications since it is generally difficult to produce very small, miniature, reserve batteries of any kind.
In addition, in certain munitions applications a relatively small amount of electrical energy, sometimes as low as 10-50 mJ is required before firing to bring up at least a portion of the onboard electronics and the like and/or to transfer firing and other information into the munitions memory and the like. In such applications, electrical energy is currently provided either by onboard electronics or by electrical energy transferred to onboard capacitors using for example induction coupling or optical or radio frequency means before the firing. In certain applications liquid reserve or thermal batteries inside the munitions are initiated to provide the required electrical energy. All such options makes the design and operation of the munitions complex, add significantly to their cost and generally require a significant amount of space onboard. The latter option also has the disadvantage of if the round is not fired within a relatively short amount of time, the initiated reserve battery can no longer provide the required amount of power and the round becomes inoperative.
A need therefore exists for alternatives to chemical reserve batteries for low power applications such as pre-fire data transfer and hold powering and for powering fuzing electronics and other similar functionalities when the required electrical energy levels are low, and for powering industrial and commercial products such as self-powered health monitoring and emergency sensor.
For munitions applications, such miniature electrical generators and power sources, hereinafter referred to as power sources, have to have a very long shelf life of up to 20 years; be low cost; and be capable of being scaled to the required power level requirements, shape and size, with minimal design and manufacturing change efforts.
A need also exist for miniature power sources for munitions applications such as gun-fired munitions, mortars and grenades in which their potential energy storage springs (elastic elements) have no stored potential energy and the required potential energy is stored in them as a result of launch acceleration.
A need also exists for miniature power sources for munitions and other industrial and commercial applications in which potential energy is stored in energy storage spring (elastic) elements of the device a priori. Hereinafter, all such mechanical potential energy storage elements (whether helical or other types of springs or elastic elements or structural flexibility) will be referred to simply as springs. A release mechanism is then used to release the stored potential energy and allow it to be converted to electrical energy via a mechanical to electrical energy conversion device such as a continuously rotating or a linear or rotary vibratory magnet and coil generator device.
A need also exists for miniature power sources that are manually operated through a push button type mechanisms provided on the surface of munitions to generate electrical energy for their pre-fire or the like powering or through said push button or toggle or other similar type of on-off mechanisms to generate electrical energy for powering various industrial and commercial low power devices. The mechanical energy to electrical energy conversion elements of such power sources may be based on magnet and coil generators or piezoelectric or any other such energy conversion devices.
An objective is to provide non-chemical miniature electrical generators and corresponding power sources for the aforementioned and the like low power applications. In these power sources, mechanical potential energy can be stored in the power source and used to generate electrical energy upon occurrence of certain events, such as firing of a projectile by a gun or by the release (or ejection) of a gravity dropped weapon or through certain manual operation. This is in contrast to chemical reserve batteries in which stored chemical energy is released upon a certain event (such as firing by a gun or by an electrical charge), thereby allowing the battery to provide electrical energy.
Another objective is to provide non-chemical power sources are miniaturized and are manually operated through a push button type mechanisms provided on the surface of munitions to generate electrical energy for pre-fire or the like powering or through said push button or toggle or other similar type of on-off mechanisms to generate electrical energy for powering various industrial and commercial low power devices.
Here, a means of storing potential mechanical energy can be elastic deformation, such as in various types of spring elements and/or the structural flexibility of the structure of the system in which it is used such as the structure of a projectile or the like, and not potential energy due to gravity. It is, however, appreciated by those skilled in the art that potential energy may also be stored by other means such as by pressurizing compressible gasses such as air. The mechanical energy may be stored a priori in the said mechanical potential energy storage springs or be manually input at the time of use. The mechanical potential energy stored in the power source storage springs can then be released via certain mechanisms to be described either upon the occurrence of certain intended event(s), such as firing and/or spinning of a projectile or releasing of a gravity-dropped weapon or other events appropriate to the device employing the power source or manually through certain mechanisms. The released potential energy can then be used to generate electrical energy using well known methods such as by the use of active materials based elements such as piezoelectric elements or magnet and coil type generators.
To this end, the mechanical stored potential energy is preferably transferred to a flywheel as kinetic energy which is then used to generate electrical energy through a continuous rotation of a rotary magnet and coil generator to achieve high mechanical energy to electrical energy conversion efficiency. Gearing mechanisms may also be employed to increase speed of generator rotation to further increase the power source energy conversion efficiency.
Alternatively, the mechanical stored potential energy is used to cause vibration of a mass-spring system. The vibration energy is then transformed into electrical energy by one of the aforementioned piezoelectric, coil and magnet or the like elements.
A second object is to provide methods and mechanisms for releasing the stored potential energy in the power sources with a priori stored mechanical potential energy. Such mechanisms include various hand operated mechanisms or various external event initiated mechanisms. Examples of such event initiated mechanisms include those operated due to gun firing acceleration; deceleration of gun-fired projectile (the so-called set-forward acceleration); the process and/or mechanism of releasing (e.g., gravity dropping) the weapon from its mounting rack or the like; pulling out or ejection of a releasing element (e.g., a releasing pin or wire); actuation or breaking of a stop element or the like via detonation of small charges; etc.
For the power sources employing piezoelectric elements for converting mechanical energy of vibration to electrical energy, methods described for mass-spring systems used in the piezoelectric based power generators described in the U.S. Pat. Nos. 7,231,874 and 7,312,557 can generally be used in the construction of the disclosed power sources, particularly for those mechanical reserve power sources to be used in gun-fired projectiles and mortars which are subject to very high-G firing acceleration levels.
In addition, in such mechanical reserve power sources, the piezoelectric elements (stacks) employed to convert mechanical energy of vibration to electrical energy may also be used as sensors to measure setback and set-forward acceleration levels, target impact impulse levels and direction, the time of such events and more as described in the U.S. Pat. No. 8,701,599 or 8,266,963 or 8,205,555 or 8,191,475 or 7,762,192 or 7,762,191.